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Composite Structures
Journal Prestige (SJR): 1.905
Citation Impact (citeScore): 5
Number of Followers: 294  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0263-8223
Published by Elsevier Homepage  [3161 journals]
  • Structural performance of FRP confined seawater concrete columns under
           chloride environment
    • Abstract: Publication date: Available online 16 February 2019Source: Composite StructuresAuthor(s): Ao Zhou, Renyuan Qin, Cheuk Lun Chow, Denvid Lau To alleviate resource shortage and environmental problems, a combination of fiber reinforced polymer (FRP) and seawater concrete is an attractive option for replacing conventional reinforced concrete in marine structures. The chloride ions in concrete structures increase with extension of service time due to penetration from the marine environment, resulting in serious deterioration of concrete structures. In order to apply such a material combination to civil infrastructure safely, the performance of FRP confined concrete with different chloride concentrations has been experimentally studied. The results show that a 23% reduction in strength is observed in 1-ply FRP confined concrete column when chloride ion concentration increases from 0% to 1.57% (saturated water level). Furthermore, a design-oriented model is proposed to evaluate the stress-strain behavior of FRP confined seawater concrete, as well as concrete with elevated chloride concentrations due to prolonged service time in the marine environment. The experimental findings and the proposed design-oriented model can promote the wide usage of FRP confined seawater concrete in offshore structures and artificial islands.
       
  • Deep drawing of fiber metal laminates for automotive lightweight
           structures
    • Abstract: Publication date: Available online 16 February 2019Source: Composite StructuresAuthor(s): T. Heggemann, W. Homberg Current challenges in the automotive industry are the reduction of fuel consumption and the CO2 emissions of future car generations. These aims can be achieved by reducing the weight of the car, which further improves the driving dynamics. In most currently mass-produced cars, the body accounts for one of the largest parts by weight, and hence designing a lightweight car body assumes great importance for reducing fuel consumption and CO2 emissions. Extremely lightweight designs can be achieved by using purely composite materials, which are very light but also highly cost intensive and not yet suitable for large scale production due to the necessity of manual processing. A promising approach for the automated, large-scale production of lightweight car structures with a high stiffness to weight ratio is the combination of high strength steel alloys and CFRP prepregs in a special hybrid material/fiber metal laminate (FML) – which can be further processed by forming technologies such as deep drawing. In current research work at the Chair of Forming and Machining Technology (LUF) at the University of Paderborn, innovative manufacturing processes are being developed for the production of high strength automotive structural components made of fiber metal laminates. This paper presents the results of technological and numerical research that is currently being performed at the LUF into the forming of hybrid fiber metal laminates. This paper focuses on the results of basic research and the individual measures (tool, process and material design) necessary for achieving the desired part quality.
       
  • Formulation of a Mixed-mode Multilinear Cohesive Zone Law in an Interface
           Finite Element for Modelling Delamination with R-curve Effects
    • Abstract: Publication date: Available online 15 February 2019Source: Composite StructuresAuthor(s): S.M. Jensen, M.J. Martos, B.L.V. Bak, E. Lindgaard A constitutive model for an interface finite element is proposed to enable simulation of delamination in composite materials with R-curve effects. The constitutive model is formulated in the framework of cohesive zone modelling (CZM). In essence, a multilinear CZ law with an arbitrary number of line segments is developed. The CZ law seeks to enable constitutive modelling of failure mechanisms on multiple scales within the fracture process zone and reduce conventional a priori assumptions regarding the shape of the CZ law. The CZ law relies on damage mechanics, an equivalent one-dimensional formulation, and criteria for mode interactions to simulate delamination under mixed-mode loading. Special emphasis is put on the derivation of interpolation formulas and a constitutive tangent stiffness tensor for the multilinear formulation. The constitutive model is implemented in the commercial FE program ANSYS Mechanical, for implicit finite element analysis (FEA), using user-programmable features. The implementation is verified through single interface element numerical studies, and its applicability is demonstrated by simulating an experiment of quasi-static delamination showing large-scale fiber bridging in pure mode I DCB glass-fiber epoxy specimens. Experimental measurements and simulation outputs using the novel cohesive element is compared to those of the conventional bi- and trilinear CZ laws.
       
  • On the use of in-situ piezoelectric sensors for the manufacturing and
           structural health monitoring of polymer-matrix composites: A literature
           review
    • Abstract: Publication date: Available online 14 February 2019Source: Composite StructuresAuthor(s): C. Tuloup, W. Harizi, Z. Aboura, Y. Meyer, K. Khellil, R. Lachat This article aims to provide a general overview of what has been achieved recently in the scientific community on the manufacturing monitoring and structural health monitoring of polymer-matrix composites (PMC) using in-situ piezoelectric sensors. Some industrial applications with the underlying issues and potential solutions will finally be discussed in the concluding section.
       
  • Dynamic assessment of base isolation systems for irregular in plan
           structures: response spectrum analysis vs nonlinear analysis
    • Abstract: Publication date: Available online 14 February 2019Source: Composite StructuresAuthor(s): Donato Cancellara, Fabio De Angelis Base isolation systems are employed in the isolation of structures by providing an efficient protection with respect to dynamic and seismic loadings. In this paper we analyze the dynamic behavior of base isolated multi-storey structures characterized by high irregularity in plan. High Damping Rubber Bearings isolators are adopted herein and they are placed in parallel with Friction Sliders isolators. For the dynamic assessment of base isolated structures in the present work two different types of dynamic analyses are investigated: a dynamic analysis with response spectrum and a nonlinear dynamic analysis. The comparative evaluation of the results obtained by performing the two different dynamic analyses has a significant importance with reference to the recent Italian seismic code. In fact when adopting the nonlinear dynamic analysis the code prescribes a mandatory comparison of the obtained results with the ones related to a dynamic analysis with response spectrum. Accordingly, the present comparative analysis is also useful to evaluate which of the two analysis is more conservative for base isolated structures and in which aspects it is more conservative. The results of the present analysis are illustrated in terms of calculations of the deformations and the stresses of the base isolated structure. For the deformations particular interest is given to the inter-storey drifts at the different levels of the multi-storey structure. For the stresses associated to the seismic loadings the interest is focused on bending moment, axial force and shear in the columns and bending moment and shear in the beams.
       
  • The average response and isotropy of 3D representative volume elements for
           random distributed short fibers reinforced elastomer
    • Abstract: Publication date: Available online 13 February 2019Source: Composite StructuresAuthor(s): Lili Chen, Boqin Gu, Jiahui Tao, Jianfeng Zhou The average response and isotropy of the 3D representative volume elements (RVEs) for random short fiber reinforced elastomer composites (SFECs) have been explored by finite element method with different fiber volume fractions (Vf) and RVE sizes. The RVEs were loaded spatially by directly applying stretches in nine loading directions and the homogenized response in each direction was obtained. The coefficient of variation of the responses of an RVE over different loading directions was used to represent the anisotropy of the RVE. The orientation tensor error was used to represent the anisotropy of all the fibers and was compared with the anisotropy of the RVEs. The simulation results for the SFRC were compared with the elastic modulus obtained by traditional empirical equations based on Halpin–Tsai estimations. The results show that the anisotropy of the RVEs decreases with the increase of the RVE size and is higher for RVEs with higher Vf. The anisotropy of the fibers decreases with the increase of the Vf. A method of averaging responses of each RVE over all loading directions greatly reduces the variation in response over different RVEs, which can be used to improve the prediction accuracy more efficient than increasing the RVE size.Graphical abstractGraphical abstract for this article
       
  • Numerical model for predicting the structural response of composite
           UHPC–concrete members considering the bond strength at the interface
    • Abstract: Publication date: Available online 13 February 2019Source: Composite StructuresAuthor(s): Hor Yin, Kazutaka Shirai, Wee Teo In this study, an improved finite element (FE) model was developed for the prediction of the structural behaviour of reinforced concrete members strengthened with ultrahigh-performance concrete (UHPC). A concrete damage model and an implicit solver in LS-DYNA were adopted in the numerical simulation. The model was calibrated and validated using experimental data. Accurately representing the interfacial bond characteristics of composite UHPC–concrete members was the primary challenge in developing the modelling technique. A novel technique using equivalent beam elements at the interface between UHPC and normal strength concrete (NSC) substrate was proposed for this purpose. The material properties of the equivalent beam elements were defined to represent the equivalent bond characteristics of NSC. The developed FE model was found to be able to effectively and efficiently predict the structural response of composite UHPC–concrete members with good accuracy.
       
  • Flexural performance of concrete beams reinforced with FRP bars grouted in
           corrugated sleeves
    • Abstract: Publication date: Available online 13 February 2019Source: Composite StructuresAuthor(s): Heng-Lei Dong, Wei Zhou, Zhenyu Wang This paper proposed to use high-strength grout and corrugated sleeves to hold FRP bars in tension zone of concrete beams, aimed at reducing crack width and improving serviceability performance. Ten large-scale simply supported beams measuring 200mm wide, 400mm depth, and 4000mm length, were tested under four-point bending. One reference beam was reinforced with steel bars and four beams were reinforced with FRP bars. Other five beams were reinforced with FRP bars grouted in sleeves in the tension zone. Test results are discussed in terms of failure modes, deflection and cracking behavior. FRP-RC beams failed by concrete crushing, achieving higher flexural capacity and larger deflection than the steel-RC beam. The use of FRP bars grouted in corrugated sleeves in tension zone of beams was an effective way to reduce crack widths and improve serviceability performance. The average bond-dependent coefficient (kb) for grouted FRP bars in sleeves was 38% lower than FRP bars surrounded by concrete. The maximum crack width at service load, which accounted for variability of crack width and long-term effect of sustained load, was less than the crack width limit of 0.7mm for beams with grouted FRP bars in sleeves but not for beams only with FRP bars.
       
  • Innovative Models for Prediction of Compressive Strength of FRP-Confined
           Circular Reinforced Concrete Columns Using Soft Computing Methods
    • Abstract: Publication date: Available online 13 February 2019Source: Composite StructuresAuthor(s): H. Naderpour, K. Nagai, P. Fakharian, M. Haji There are several methods for predicting experimental results such as empirical methods, elasticity and plasticity theory. Among these methods, the use of soft computing has been expanded due to good capabilities and high accuracy in predicting the target. Soft computing contains computational techniques and algorithms to provide useful solutions to deal with complex computational problems. In this study, three methods including Artificial Neural Networks, Group Method of Data Handling and Gene Expression Programming are utilized to predict the compressive strength of columns confined with FRP. Total of 95 experimental data were selected to form the model. The height of the column, the compressive strength of unconfined concrete, the elastic modulus of FRP, the area of longitudinal steel, the yield strength of longitudinal steel and confinement pressure provided by FRP and transverse steel were considered as input parameters, while the compressive strength of FRP-confined columns was considered as the target. The proposed methods are compared with the existing models and provide great accuracy in predicting the results. Among the utilized methods, the ANN model showed the highest accuracy.
       
  • Effect of Basalt Fibers on the Flexural Behavior of Concrete Beams
           Reinforced with BFRP bars
    • Abstract: Publication date: Available online 13 February 2019Source: Composite StructuresAuthor(s): Farid Abed, Abdul Rahman Alhafiz This research investigates experimentally the effects of adding different types of fibers to the concrete mixes on the flexural behavior of concrete beams reinforced longitudinally with BFRP bars. The main aim is to study the feasibility of using newly developed basalt microfibers to improve the concrete response. Twelve beams were prepared and cast using plain, basalt fibers, and synthetic fibers-reinforced concrete (FRC) with a 40MPa target compressive strength. Basalt fibers of two different lengths of 24mm and 12mm were considered. Flexural tests were conducted on each of the BFRP-FRC beams using a four-point test setup. The test matrix also included FRC beams reinforced with GFRP bars as well as conventional steel rebar for comparisons. Results showed that introducing basalt fibers to the concrete increased curvature ductility of these beams. A noticeable improvement in the flexural capacities was also recorded due to the delay in concrete failure strain (beyond 0.003) at the compression zone, which helped the BFRP bars attained a higher ultimate strength. The opening of cracks and their deep propagation was effectively restrained by the bridging effect of the basalt fibers, which kept the crack widths lower than the allowable limit of 0.7 mm at service.
       
  • Mechanical behaviour of a sandwich panel composed of hybrid skins and
           novel glass fibre reinforced polymer truss core
    • Abstract: Publication date: Available online 13 February 2019Source: Composite StructuresAuthor(s): Khaled Djama, Laurent Michel, Aron Gabor, Emmanuel Ferrier This study investigated the usability of hybrid sandwich structures as facade panels. The explored sandwich structure was made of mineral-glass fibre reinforced polymer (GFRP) skins and a GFRP truss core, fabricated by means of a novel manufacturing method. The compressive and shear specific strengths of the panels were assessed and compared with a few common lightweight structures to verify that the manufactured truss core had comparable values. Three-point bending tests indicated that the polyurethane foam used (required for the manufacturing process) had negligible mechanical contribution. Full-scale panels were tested under a distributed load. The tests were simulated using the three-dimensional finite element method to predict the pressure at which mineral cracks appeared in order to avoid their occurrence in the design phase. The simulation results exhibited good agreement with experimental data, and the model was validated in terms of deflection and strain responses. The occurrence of cracks and their propagation were numerically reproduced using the concrete-damage plasticity model. The link between the connector and crack positions in the mineral skin was highlighted in this study.
       
  • Influence of production based surface topography and release agent amount
           on bonding properties of CFRP
    • Abstract: Publication date: Available online 13 February 2019Source: Composite StructuresAuthor(s): M. Mund, K. Lippky, D. Blass, K. Dilger The application of carbon fiber reinforced plastics (CFRP) has increased in recent years. Besides aerospace applications, automotive industry relies on those materials as they offer the possibility to reduce component weight significantly. A main challenge is the joining of those materials. Due to several advantages, adhesive bonding has been established as the preferred joining method for CFRP. The adhesive bonding process is challenging as the surfaces of CFRP are not suited for adhesive bonding. On one hand, the resulting CFRP-parts have smooth surfaces preventing mechanical interlocking with the adhesive and on the other hand, the release agent is transferred from the mold to the surface of the CFRP contaminating the surface. The resulting surfaces are generally inappropriate to achieve structural and durable bonds, making a surface pre-treatment inevitable.As an alternative approach, this study focuses on the manufacturing method for CFRP with surfaces suitable for adhesive bonding without an additional surface pre-treatment. Therefore, the amount of release agent is varied to achieve a low degree of contamination and laser-structured molds are used resulting in CFRP with varying surface topographies. The surfaces of the CFRP-plates are analyzed. Then the influence of the varied parameters on the bonding strength is investigated by lap-shear tests.
       
  • On the vibration of size dependent rotating laminated composite and
           sandwich microbeams via a transverse shear-normal deformation theory
    • Abstract: Publication date: Available online 12 February 2019Source: Composite StructuresAuthor(s): Armagan Karamanli, Metin Aydogdu In this paper, the eigenfrequencies of rotating laminated composite (LC) and sandwich microbeams with different boundary conditions (BCs) are studied. The size-dependent variational formulation of the problem is obtained based on the Modified Couple Stress Theory (MCST) by employing a transverse shear-normal deformable beam theory and finite element method (FEM) formulation. The convergence and verification studies of the developed code are carried out and computed results in terms of dimensionless fundamental frequencies (DFFs) are compared with the available ones in the open literature. Various BCs, aspect ratios, fiber orientation angles, thickness to material length scale parameter (MLSP) ratios, core thickness to face layer thickness ratios, dimensionless rotation speeds (DRSs) and hub ratios are employed for the extensive analyses. It is found that the DFFs of the LC microbeams are highly affected by the small size effect accompanying with the orthotropy ratios, DRSs, hub ratios and fiber orientation angles. The effect of the small size on the DFFs of the rotating clamped-clamped LC microbeams is more pronounced than on those of the rotating clamped-free LC microbeams. The hub ratio has a significant effect on the DFFs of the rotating LC microbeams than the rotation speed.
       
  • Tailored fibre placement of commingled carbon-thermoplastic fibres for
           notch-insensitive composites
    • Abstract: Publication date: Available online 11 February 2019Source: Composite StructuresAuthor(s): H.M. El-Dessouky, M.N. Saleh, M. Gautam, G. Han, R.J. Scaife, P. Potluri Tailored fibre placement (TFP) is an embroidery-based technology that allows the fibre tows to be placed exactly where they are most needed for structural performance and stitched into position on a compatible textile or polymer substrate. In this study commingled carbon-nylon fibre tows were utilised to produce thermoplastic cross-ply net-shaped preforms using TFP. Four TFP composite plaques were manufactured; baseline (blank), machined-hole, tailored-hole-1 and tailored-hole-2. Steering the tows was used to create the hole in tailored-hole-1 and tailored-hole-2. In comparison to the design of tailored-hole-1, a different fibre trajectory, with a circular reinforcement around the hole, was suggested for the tailored-hole-2. Fibre volume fraction, optical microscopy, X-ray-CT scans, tensile and open-hole tests were carried out. With the exception of the baseline sample, the modified design of tailored-hole-2 composite exhibited the highest axial strength and modulus compared to the machined-hole and tailored-hole-1 composites. Only the tailored-hole-2 specimens exhibited less than 10 % reduction of the notched strength compared to the un-notched strength. This study highlights the importance of the stress/load-paths and associated fibre-orientations. While TFP can be an extremely valuable design tool for composite preforms and resulting structural components, a deep understanding of stress distributions is inevitable to achieve optimal TFP-design.
       
  • Polymer Concrete Periodic Meta-structure to enhance Damping for Vibration
           Reduction
    • Abstract: Publication date: Available online 11 February 2019Source: Composite StructuresAuthor(s): Semin Kwon, Sangkeun Ahn, Hyo-In Koh, Junhong Park Polymer concrete is a mixture of polymeric resin and aggregates, which is superior in strength, durability and dynamic characteristics compared with general cement concrete. This study presents a complex periodic structure composed of the cement concrete embedded with periodic arrangement of polymer concrete. The experiments and vibration analysis were carried out to determine the dynamic properties and flexural strength of the complex concrete according to embedment structure of polymer concrete. The specimens of the complex concrete beam were fabricated of cylindrical and wave-pattern polymer concrete embedment with small volume fraction. The dynamic properties of the complex concrete specimens were measured by the vibration experiments in the audio frequency. The flexural strength of each specimen was measured by the three-point bending test to confirm structural safety. The analytical model was presented to describe the vibration response and modal damping ratio of the complex concrete beam. The effects of periodic structure on the complex concrete beam were identified as an efficient methodology resulting in large vibration reduction with small polymer volume fraction.
       
  • Analytical Modeling of Multi-sectioned Bi-stable Composites: Stiffness
           Variability and Embeddability
    • Abstract: Publication date: Available online 11 February 2019Source: Composite StructuresAuthor(s): Janav P. Udani, Andres F. Arrieta Multi-stable composite laminates have been widely investigated for morphing applications due to distinct geometrical characteristics about each stable configuration. Recently, a mechanism for realizing on-demand stiffness adaptation in compliant structures has been proposed exploiting the stiffness variation from switching between the stable states of embedded bi-stable laminates. This allows for reducing the coupling between loading and morphing deformation modes, broadening the overall design space for morphing structures. However, the design of such embeddable laminates requires the study of multiple lamination domains to allow embedding within larger compliant structures. This process is currently done by computationally expensive simulations. We present an analytical model to predict the stable shapes and structural characteristics of multi-section, multi-stable composite laminates subject to two clamped boundary conditions. The analysis is conducted employing the Rayleigh-Ritz method using polynomial approximations of the displacement fields. The structural characteristics are predicted while constraining the laminate edges, thus extending previous models designed to account mainly for free edge boundary conditions. Our model is subsequently applied to explore the design space for characterizing the stability and variable stiffness properties of two different classes of bi-stable laminates. The presented model allows for the efficient design of multi-stable laminates embeddable within compliant structures.
       
  • Analytical and numerical modeling of rc beam-column joints retrofitted
           with frp laminates and hybrid composite connectors
    • Abstract: Publication date: Available online 11 February 2019Source: Composite StructuresAuthor(s): Ayman Mosallam, Khaled Allam, Mohamed Salama This paper summarizes results on an analytical and numerical simulation of structural behavior of reinforced concrete (RC) beam-column joints retrofitted with different types of fiber-reinforced-polymeric (FRP) composite laminates and hybrid connectors. In this study, non-linear numerical simulations for the behavior of reinforced concrete (RC) beam-column joints that were evaluated in another phase of this study. The behavior of a total of eight full-scale interior RC beam-column specimens were numerically evaluated. The interior reinforced concrete (RC) beam-column joint specimens were subjected to both simulated gravity and low-frequency full-cyclic reversal loads. For repair and external strengthening applications, three systems are evaluated including high-strength carbon/epoxy composite laminates, high-modulus carbon/epoxy laminates and E-glass/epoxy external laminates. For bond-slip retrofit, the light-weight hybrid composite connector, developed by the principal author, was evaluated through large-scale tests and is molded numerically. Good correlation between numerical and experimental results is achieved. A comparison between the numerical and experimental results are also presented.
       
  • Modelling the different mechanical response and increased stresses
           exhibited by structures made from natural fibre composites
    • Abstract: Publication date: Available online 11 February 2019Source: Composite StructuresAuthor(s): J.M.F.A. Blanchard, U. Mutlu, A.J. Sobey, J.I.R. Blake Natural fibres exhibit improved sustainability and similar mechanical properties to E-glass. However, for laminates there is a larger difference in properties and limited assessments of structural components. An analytical method for grillages is developed which is generally shown to predict the stress to within 5% of an FEA model. The simulations demonstrate a change in structural response between flax and carbon, with flax demonstrating higher stresses than expected for the lower Young’s modulus for the same topology. Flax is shown to be more sensitive to transverse Young’s modulus than standard composites and a better characterisation of this property is required.
       
  • Fatigue Behavior Analysis and Multi-Scale Modelling of Chopped Carbon
           Fiber Chip-Reinforced Composites under Tension-Tension Loading Condition
    • Abstract: Publication date: Available online 11 February 2019Source: Composite StructuresAuthor(s): Haibin Tang, Guowei Zhou, Zhangxing Chen, Li Huang, Katherine Avery, Yang Li, Haolong Liu, Haiding Guo, Hongtae Kang, Danielle Zeng, Carlos Engler-Pinto, Xuming Su In present study, the fatigue damage behavior of chopped carbon fiber chip-reinforced composite has been experimentally and numerically investigated. A large scatter is exhibited in the S-N diagram due to the random distribution of carbon fiber chips, and therefore a new analysis procedure is proposed to link the local microstructure to the fatigue behavior of the bulk material. Interrupted fatigue tests are also performed so that microstructure characterization can be conducted on the tested samples to analyze the crack initiation and propagation. Inspired from the experimental findings, a multi-scale progressive damage fatigue model is proposed to predict the fatigue behavior. The model incorporates a new stochastic chip-packing algorithm for microstructure reconstruction along with continuum damage models into the representative volume element (RVE) model in ABAQUS/Explicit. The simulation results based on the proposed model are in good agreement with the experimental data in terms of cracking modes and predicted life.
       
  • Aging condition identification of viscoelastic sandwich structure based on
           empirical wavelet transform and Hilbert envelope demodulation
    • Abstract: Publication date: Available online 11 February 2019Source: Composite StructuresAuthor(s): Yue Si, Zhousuo Zhang, Lingfei Kong, Shujuan Li, Quandai Wang, Chuiqing Kong, Yan Li Viscoelastic sandwich structures (VSSs) have been widely used in mechanical equipment. The aging condition monitoring of VSSs is essential for fault prevention of mechanical equipment. However, the ageing condition identification of VSS is still a challenging task since the change of structural response caused by the ageing of viscoelastic sandwich structure (VSS) is very puny. Therefore, a novel identification method based on empirical wavelet transform (EWT) and Hilbert envelope demodulation is proposed for the ageing condition identification of VSS. First, EWT is constructed to decompose the vibration response signals of VSS into a set of sub–band signals, so that the aging condition feature components are allocated in a certain frequency band. Second, the sub–band signals that contain rich aging condition information are selected and used to reconstruct a new signal. Thirdly, the reconstructed signal is analyzed with Hilbert envelope demodulation to obtain an envelope spectrum. Finally, the low band energy of envelope spectrum is calculated as detection index to identify the aging condition of VSS. The proposed method is verified with a well-designed VSS in which the viscoelastic core subjected to accelerated ageing in a thermal-oxygen ambient. The results show the outstanding performance of the proposed method.
       
  • Anisotropy compensated MUSIC algorithm based composite structure damage
           imaging method
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Qiao Bao, Shenfang Yuan, Yanwen Wang, Lei Qiu Multiple signal classification (MUSIC) algorithm is a promising method in guided wave based structural health monitoring (SHM) area because of its directional scanning ability and easy arrangement of the sensor array. However, since composite structures are anisotropic, guided waves have different velocities along different directions, i.e. propagation anisotropy. For different scanning positions of the monitoring area in MUSIC algorithm, the directions from the scanning position to the sensor array are different. Even for the same scanning position, the directions from the scanning position to each element in the sensor array are also different. If a fixed velocity is used in MUSIC algorithm, there must exist sensor phase errors in steering vectors of MUSIC algorithm caused by structural anisotropy, as well as the sensor position error, resulting in the localization error. To reduce the localization error caused by sensor phase errors, an anisotropy compensated MUSIC algorithm is proposed, which could compensate different kinds of sensor phase errors jointly and improve the localization precision and reliability of MUSIC algorithm. The proposed method is verified on a reinforced composite panel with one T-stiffener. Experimental results show that the proposed method can realize damage localization with an obviously improved accuracy.
       
  • Low-frequency broadband absorption of underwater composite anechoic
           coating with periodic subwavelength arrays of shunted piezoelectric
           patches
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Zhifu Zhang, Yizhe Huang, Qibai Huang This paper proposes an underwater semi-active composite anechoic coating with periodic subwavelength piezoelectric arrays to broaden the low-frequency absorption bandwidth and improve the absorption coefficient. Based on the effective medium method, the dual equivalent properties for the volume density and Young’s modulus of the equivalent thin-plate interlayer are computed. Then, a complete two-dimensional theoretical model for oblique incidence is established by combining the shunt damping technique and wave propagation theory in layered media. On the premise of strictly satisfying the two preconditions of subwavelength assumption and stratified convergence criteria, the correctness and effectiveness of the present model are confirmed by successively according to the finite element simulation results, experimental data, and theoretical predictions. At last, change regulations of seven critical parameters on the sound absorption characteristics of the present coating are investigated to reveal the multiple energy dissipation mechanisms of the overburden in the whole research frequency band.
       
  • Optimizing thermographic testing of thick GFRP plates by assessing the
           real energy absorbed within the material
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Jan P. Müller, Rainer Krankenhagen Active thermography is a well suited non-destructive testing method for the challenging inspection of wind rotor blades. Since the GFRP structures are up to some centimetres thick, long pulse heating is required to provide an appropriate energy input into the structure. So far, no best practice exists to guarantee a reliable detection of deep-lying flaws. In this work, a step wedge specimen having a maximum thickness of 34 mm is systematically investigated by experiment and well-matched simulations to assess the influence of the experimental parameters, like the absorbed energy, on thermal contrasts. Finally, a scheme to conduct full-scale test of a wind rotor blade in less than three hours is proposed.
       
  • Effect of cutter geometry on machining induced damage in orthogonal
           cutting of UD polymer composites: FE study
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): F. Cepero-Mejías, J.L. Curiel-Sosa, C. Zhang, V.A. Phadnis This article presents a finite-element analysis (FEA) based study to understand the influence of cutting parameters (rake angle, relief angle and cutter edge radius) on the machining-induced damage of unidirectional (UD) composites. Carbon/epoxy (CFRP) and glass/epoxy (GFRP) composites are considered. Onset of damage in composites is modelled using a combination of maximum stress and Puck’s fracture criteria, while a novel damage propagation algorithm is proposed to account for the post-damage material softening behaviour. A spring-back phenomenon (partial elastic recovery of workpiece material after tool passed a cutting surface) often observed in composites machining, is considered in the FE model to allow a better prediction of the thrust force and induced damage. A validated FE model predicts that with increasing relief angle, the extent of sub-surface damage is reduced. Rake angle or tool edge radius are not found to have a great influence on the induced damage. A large dependence is observed between the fibre angle and the induced damage, as the severity of damage increase when fibre orientations varies from 30° to 90°.
       
  • Low-velocity Impact Resistance Behaviors of Bio-inspired Helicoidal
           Composite Laminates with Non-Linear Rotation Angle based Layups
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Hongyong Jiang, Yiru Ren, Zhihui Liu, Songjun Zhang, Zheqi Lin Through evolutionary process, special biological structures (e.g. micro- or macro-scale helicoidal laminated structures) are formed naturally to resist natural enemies. With some bionic inspirations, anti-impact design of composite laminates applied for aerospace, vehicle, etc. can be stimulated by helicoidal biological structures. In the work, the Non-Linear Rotation Angle(NLRA) based bio-inspired helicoidal layups are designed to enhance the impact resistance capacity of composite laminate. Four types of helicoidal configurations are proposed including Quasi-isotropic(QI), Helicoidal-Recursive(HR), Helicoidal-Exponential(HE) and Helicoidal-Semicircular(HS). The failure behaviors of material are investigated with the progressive damage model. Damage development of fiber, matrix and delamination interface is conducted with stress-based failure criteria, fracture energy criteria and stiffness degradation method. The impact damage behaviors of carbon/epoxy composite laminates with QI and NLRA helicoidal layups are studied and compared. Further, effects of coefficients in each layup formula are discussed. Numerical results show that predicted load-time curve and damage modes for QI correlate well with experimental results. It is revealed that both the maximum resistance load and threshold load for the initial matrix damage and delamination increase with the increase of each coefficient. As compared with QI layup, HR and HE layups with large rotation angles can improve the capacity of impact resistance.Graphical abstractGraphical abstract for this article
       
  • Effect of hygrothermal aging on the quasi-static behaviour of CFRP joints
           varying the overlap length
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): J.J.M. Machado, E.A.S. Marques, A.Q. Barbosa, Lucas F.M. da Silva Adhesively bonded joints with composite substrates are crucial for the manufacture of lightweight structural components for the automotive industry. However, the safety of the vehicles must still be ensured after hygrothermal aging of both composite substrates and adhesive, as adverse conditions such as moisture and temperature will be a constant during a vehicle lifecycle. This work studies the influence of hygrothermal aging and temperature on the quasi-static behaviour of adhesive joints made with unidirectional composite substrates and a crash resistant adhesive using different overlap lengths. A complementary numerical simulation was performed to model both the water uptake processes and the failure process of moisture affected materials. Both the simulation and the experimental data showed increased susceptibility to delamination failure induced by water absorption in the composite and changes in the adhesive properties.
       
  • The behaviour of compressed plate with a central cut-out, made of
           composite in an asymmetrical arrangement of layers
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Katarzyna Falkowicz, Hubert Dębski, Paweł Wysmulski, Patryk Różyło The study investigated thin carbon/epoxy composite plate elements with a central cut-out of regular shape, under uniform compression. The aim of the study was to investigate the possibility of using these elements as elastic elements whose stiffness depends on tailoring the cut-out geometry and laminate ply orientation. To ensure stable operation of the structure in the postbuckling range, the plate was assigned the properties of an unsymmetrical lay-up with extension-twisting and extension-bending couplings. The structure was analysed numerically by the finite element method. The scope of numerical simulations included linear analysis of an eigen problem using procedures for geometrically nonlinear analysis and the commercial simulation software ABAQUS®. The aim of the analysis was to determine a laminate ply orientation generating the lowest buckling mode (flexural-torsional) in order to ensure stable operation of the structure in the postbuckling range.
       
  • A Novel Cylindrical Negative Stiffness Structure for Shock Isolation
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Xiaojun Tan, Bing Wang, Shuai Chen, Shaowei Zhu, Yuguo Sun The negative stiffness (NS) metamaterial is a promising material that has attracted a great amount of interest. Many types of NS structures have been proposed and investigated. However, almost all of the previously proposed structures were cuboidal, which is undesirable for certain special engineering applications. In this paper, a cylindrical NS structure composed of spatial curved beams is proposed, and can potentially be applied to shock isolation, vibration control, and deployable structures. Specimens were fabricated using Fused Deposition Modeling (FDM) technology. The influence of the structural parameters on the NS property was investigated, and the criteria for the structure to achieve snap-through behavior were obtained. Impact tests were performed to investigate the structure’s cushion performance. The results of the impact tests revealed that the structure achieved good cushion performance by thresholding the magnitude of the acceleration response, when the snap-through behavior occurred.
       
  • Effect of drilling-induced damage on the open hole flexural fatigue of
           carbon/epoxy composites
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Andreas Haeger, Manuel Grudenik, Michael J. Hoffmann, Volker Knoblauch Conventional drilling is the most common machining process done on carbon fibre reinforced polymers (CFRP). However, the effect of machining-induced damage on the mechanical performance and reliability of structural composite parts is not fully understood yet. Therefore, this study contributes by a detailed investigation of the open hole bending (OHB) fatigue behaviour of quasi-isotropic CFRP T800S/M21 under consideration of the machining quality. Holes in different qualities were generated with new and worn-off tools. Afterwards, the effect of machining quality on stiffness degradation was analysed in OHB fatigue tests up to 107 cycles. Typical failure modes in dependence of the loading level are reported and discussed with respect to the fatigue life data and the presence of drilling induced delamination. Comprehensive ex-situ analysis by computed tomography were performed in order to characterise both, the fatigue behaviour and its relation to machining caused delamination damage. The results reveal a negative impact of machining defects on lifetime in the early stage of fatigue, whereas this effect vanishes for high levels of stiffness degradation. Several indicators for the promotion of fatigue crack propagation due to pre-damage after the drilling process are identified for moderate flexural loading situations.
       
  • Structural performances of pultruded gfrp emergency structures - part 1:
           experimental characterization of materials and substructure
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): L. Cavaleri, M. Di Paola, M.F. Ferrotto, T. Scalici, A. Valenza This paper presents an experimental study in the field of structures made of pultruded fiber reinforced polymers (FRP) elements to be used for emergency purposes. A preliminary design of a 3D pultruded glass fiber reinforced polymer structure is presented with the mechanical characterization of the constituting elements. The axial and flexural properties of laminate and I-shaped GRFP profiles are discussed considering the short term creep. In a companion paper, the benefits, the limits and the reliability of the structure analyzed for emergency applications are discussed. In details, the numerical structural analysis of the full-scale 3D model is described followed by the experimental assessment of the structural capacity by a full-scale 2D model.
       
  • An investigation of repair methods for delaminated composite laminate
           under flexural load
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Byeong-Su Kwak, Gwang-Eun Lee, Gyu-Seok Kang, Jin-Hwe Kweon The delamination failure of a composite laminate under a flexural load was repaired by micro-bolts and adhesive resin. The specimens were made by autoclave processing, and in the prepreg-stacking step, a Teflon release film was inserted to mimic the delamination in the specimens. Bolts made with brass or steel were used in the micro-bolt repair method, and the diameters of bolts were 0.6, 1.0, and 1.2 mm. For the resin injection repair method, the EA9396, a low-viscosity and room-temperature curing epoxy adhesive, was used as the repair material. In the case of the micro-bolt repair method, although the larger bolt resulted in higher bending strength, the difference in bending strength of the repaired specimens, depending on bolt diameter, was insignificant. The difference in bending strength was only 21% when 0.6-mm and 1.2-mm diameter bolts were installed. On the other hand, the bending strength of the specimens, repaired by the resin injection method, was recovered, up to 93% of the pristine specimen. From the results of this study, it was confirmed that the resin-injection repair, which injects resin into the delamination to bond the entire separated surface area, is more effective than using micro-bolts if the flexural load is predominant.
       
  • Biaxial constitutive relationship and strength criterion of composite
           fabric for airship structures
    • Abstract: Publication date: Available online 10 February 2019Source: Composite StructuresAuthor(s): Taibai Shi, Wujun Chen, Chengjun Gao, Jianhui Hu, Bing Zhao, Ping'an Wang, Mei Wang Given their irreplaceable advantages such as high strength-to-weight ratio, composite fabrics have been widely applied and studied. However, due to the limitation of specimen design and test procedure, integral biaxial constitutive relationships and valid failure criteria of composite fabrics were unavailable while desirable. In this study, typical composite fabrics for airship structures were employed to manufacture self-designed double-layer cruciform specimens as biaxial tensile tests were performed subsequently. Since the stiffness of the specimen was reasonably distributed, biaxial tensile failure characterizing the biaxial tensile strength under various warp-to-weft stress ratios was acquired. Two failure modes, the cross slits rupture and the single slit breakage, occurred when specimens reached load-bearing capacities. Furthermore, the digital image correlation approach was utilized to record the strain field during the whole test process. According to the test data, integral stress-strain curves and analytical biaxial stress-strain response surfaces were calibrated, developed and interpreted thoroughly. Since significant deviation was observed in previous failure criteria for rigid composite materials, a novel biaxial failure criterion was firstly proposed which could perfectly comply with the failure envelope obtained from the test results. As the accuracy of the failure criterion was verified, physical, mechanical and mathematical explanations for the novel failure criterion were finally illustrated.
       
  • Understanding progressive failure mechanisms of a wind turbine blade
           trailing edge section through subcomponent tests and nonlinear FE analysis
           
    • Abstract: Publication date: Available online 8 February 2019Source: Composite StructuresAuthor(s): Xiao Chen, Peter Berring, Steen Hjelm Madsen, Kim Branner, Sergei Semenov This paper presents a comprehensive study on structural failure of a trailing edge section cut from a composite wind turbine blade. The focus is placed on understanding progressive failure behavior of the trailing edge section in subcomponent testing during its entire failure sequence. Digital Image Correlation (DIC) is used to capture buckling deformation and strain distributions of the specimen. Detailed post-test inspection is performed to identify failure modes and failure characteristics. A nonlinear Finite Element (FE) model that accounts for all observed failure modes is developed based on continuum damage mechanics and progressive failure analysis techniques. Multiple structural nonlinearities originate from buckling, and contact and material failures are included in the model to predict the failure process. The study shows that in addition to the buckling-driven failure phenomenon, the surface contact of sandwich panels contributes to the failure process of the trailing edge section. Foam materials start to fail before the ultimate load-carrying capacity of the specimen is reached, while both composite materials and adhesive materials fail in the post-peak regime. The matrix-dominant failure and delamination develop before the fiber-dominant failure in composite laminates. The proposed FE model captures the progressive failure process of the trailing edge section reasonably well.
       
  • Study of the interlaminar fracture under mode I loading on FFF printed
           parts
    • Abstract: Publication date: Available online 8 February 2019Source: Composite StructuresAuthor(s): J. Fonseca, I.A. Ferreira, M.F.S.F. de Moura, M. Machado, J.L. Alves The present study aims the development of a methodology for the analysis and evaluation of the fracture toughness under mode I loading of 3D printed parts, produced by the fused filament fabrication (FFF) additive technology. This work is motivated by the urgent need of improvement in this area, in order to extend the reliability of this process to applications which require high mechanical performance. For this purpose, a specific geometry was developed, taking into account the inherent characteristics of both, the applied material and process used for the production of double cantilever beam (DCB) tests. A set of experimental tests was performed with pure and short fibre reinforced Polyamide 12 (PA 12), and, in parallel, a numerical analysis was also followed for each series. Posteriorly, an inspection on the fracture surfaces was made, by microscopy, in order to refine the conclusions obtained and furtherly comprehend the variables in play. The obtained results provided a consistent value for the fracture toughness for only one of the cases studied, being this the unreinforced material. However, for the reinforced material, a set of conclusions which justify its behaviour was also able to be attained. The followed approach for the numerical analysis also revealed to be as suitable for this specific combination of material and additive process.
       
  • Structural performances of pultruded gfrp emergency structures - part 2:
           full-scale experimental testing
    • Abstract: Publication date: Available online 8 February 2019Source: Composite StructuresAuthor(s): L. Cavaleri, M. Di Paola, M.F. Ferrotto, A. Valenza This paper presents an experimental testing of a pultruded glass fiber reinforced polymer (FRP) structure used for emergency applications continuing the discussion presented in a previous paper (part 1) where the study of the characteristics of material and elements are presented. First, the design of the composite structure and components and the evaluation of the structural behavior by means of numerical and analytical approach according to current regulatory codes are described. In this frame, the global and local response was observed according to load paths deriving from the design loads at limit states. Then, the experimental test on a full-scale 2D model is presented at different load configurations up to the failure of the composite structure, comparing the experimental results with the load capacity predicted by the numerical model. The results indicate that the high performances of the structure provide a very good capacity in view of facing service loads and also in extreme conditions. Moreover, it was observed that the actual capacity obtained by the experimental test is much higher compared to the bearing capacity provided by the design according to current technical codes.
       
  • Layered Composite Entangled Wire Materials Blocks as Pre-Tensioned
           Vertebral Rocking Columns
    • Abstract: Publication date: Available online 7 February 2019Source: Composite StructuresAuthor(s): Mohammad M Kashani, Ehsan Ahmadi, Alicia Gonzalez-Buelga, Dayi Zhang, Fabrizio Scarpa This work focuses on entangled wire materials as an option for use between segments of a novel self-centring bridge pier inspired from the human spine mechanism to increase energy dissipation capability of the pier in rocking. A comprehensive set of free-decay vibration tests was conducted on small-scale columns with and without entangled wire materials. Wooden blocks are used as vertebrae with entangled wire materials as intervertebral disks. The whole system is tied together using a pre-tensioned tendon. Dynamic properties of columns (i.e. frequency and damping ratio) were then identified and compared. It is found that the use of entangled wire materials significantly increases the energy dissipation capacity of the system during rocking. This finding is very encouraging for future use of entangled wire materials composite systems in large-scale testing of the proposed rocking column, while their shear and axial stiffness needs be improved to reduce large shear and axial deformations.
       
  • Manufacturing and characterization of novel clutch non-conventional
           fiber-reinforced composite laminates
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): Cyrus Vakili Rad, Frank Thomas, Brandon Seay, Michael JL van Tooren, Subramani Sockalingam In this study the manufacture and characterization of novel non-conventional composite laminates coined as clutch laminates are presented. These carbon/epoxy laminates are manufactured using prepreg slit tape in an automated fiber placement (AFP) machine through tow skips. The AFP process allows for the tailoring of material architecture, resulting in woven-like structures without the need for a loom. These laminates are heterogeneous due to variation of fiber orientation and therefore, the material properties at a given section is a function of in-plane spatial coordinates. The thermal and mechanical behavior is studied where the clutch laminate lay-up pattern is represented with a sub cell approach utilizing 3D shell finite elements where the tows are deposited onto the regions mimicking the AFP course. Experimental results show that post-cure thermal warpage for the clutch carbon/epoxy laminates is significantly reduced when compared to conventional asymmetric laminates while also exhibiting tensile properties comparable to traditional laminates of the same ply counts. Based on the model predictions, the reduction in the warpage is attributed to the spatial variations in the local stacking sequences leading to reduced net deformation.
       
  • High performance functional composites by in-situ orientation of carbon
           nanofillers
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): G. Singer, G. Sinn, H. Rennhofer, R. Schuller, T.A Grünewald, M.M. Unterlass, U. Windberger, H.C. Lichtenegger A simple route for the in-situ orientation of carbon nanofillers applied during the curing process of a carbon fiber reinforced polymer (CRFP) in a hot press, is demonstrated. Neat MWCNT, amine-functionalized MWCNT (MWCNT–NH2) and CNF were dispersed in an epoxy resin using a three-roll-mill (TRM) to ensure good dispersion. The process leads to a hierarchically structured functional composite where MWCNT/CNF are aligned in the z-direction (out-of-plane) of the carbon fiber plies, giving rise to improved mechanical and electrical performance. Our results demonstrate that aligned carbon nanofillers yield significantly more pronounced improvements than non-oriented fillers. An applicable processing route towards advanced functional composite materials with major practical importance is presented in this study.
       
  • A wave-based numerical scheme for damage detection and identification in
           two-dimensional composite structures
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): R.K. Apalowo, D. Chronopoulos Previous studies on wave inspection in different propagation directions have focussed on the analysis of wave propagation and wave scattering from various types of joints in two-dimensional monolayered structures. In this work, a Finite Element (FE) based numerical scheme is presented for quantifying wave interaction with localised structural damage within two-dimensional layered composite structures having arbitrary layering, complexities and material characteristics. The scheme discretise a damaged structural medium into a system of N healthy substructures (waveguides) connected through a joint which bears the localised structural damage/discontinuity. Wave propagation constants along different propagation directions of the substructures are sought by combining Periodic Structure Theory (PST) and the FE method. The damaged joint is modelled using standard FE approach, ensuring joint-substructures mesh conformity. This is coupled to the obtained wave propagation constants in order to determine scattering coefficients for the wave interaction with damage in different propagation directions within the structure. Wave interaction coefficients for different damage types and structural parameters are analysed in order to establish an optimum basis for detecting and identifying damage, as well as assessing the orientation and extent of the detected damage. The main advantage of this scheme is precise predictions at a very low computational cost.
       
  • A phase field approach to simulate intralaminar and translaminar fracture
           in long fiber composite materials
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): A. Quintanas-Corominas, J. Reinoso, E. Casoni, A. Turon, J.A. Mayugo The development of predictive numerical methods, which accurately represent the progressive failure of long fiber composite materials, is nowadays required for the achievement of optimized mechanical responses in terms of load bearing capacities of modern composite structures. In this investigation, two characteristic failure mechanisms of long fiber composites, denominated as intralaminar and translaminar fracture, are simulated by means of a novel version of the phase field approach of fracture. This numerical strategy encompasses a sort of gradient-enhanced damage formulation rooted in the Griffith theory of fracture, which is herewith extended for its use in composite laminates applications. In order to assess its verification and validation, the predictions obtained using the present formulation are compared against experimental results and two well-established alternative computational methods, which correspond to an anisotropic local-based continuum damage model and a cohesive zone model. The comparisons demonstrate that the PF approach with the proposed formulation provides reliable and robust predictions under quasi-static loading, but with a higher versatility regarding the potential of triggering arbitrarily complex crack paths with intricate topology over alternative techniques.
       
  • Numerical Investigation of Composite Laminate Subjected to Combined
           Loadings with Blast and Fragments
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): Jintao Li, Chao Huang, Tian Ma, Xiancong Huang, Weiping Li, Moubin Liu Composites are considered as effective materials in absorbing the energy of blast and impact, and have been often used in complex loading environments. A numerical model is developed to analyze the response and damage of S-2 glass/SC-15 epoxy composite laminate subjected to combined loadings with blast and fragments. A composite progressive failure model is used to investigate the damage and the failure of the material. The proposed numerical model is validated by its comparison with the experimental data obtained from the literature. Three different types of loading combinations: (1) ammunition fragments impact loading, (2) bare blast loading, and (3) the combinations of blast and fragments loading, correspond to the scenarios of the near-field and the far-field explosions. Moreover, the response and the damage evaluation of the composite are analyzed here. It is concluded that the damage modes of the laminate are correlated to the type of the loading. Furthermore, the synergetic effects for the composite laminate subjected to the combined blast loading and the fragments impact are verified and evaluated. By comparing the energy absorption and the damage zone in the laminate, the synergetic effect is attributed to the conjunction of damage and the continuous pressure of the detonation products.
       
  • Impact damage assessment in polymer matrix composites using self-heating
           based vibrothermography
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): Andrzej Katunin, Angelika Wronkowicz-Katunin, Dominik Wachla Low-velocity impact damage (LVID) is one of the most dangerous damage types appearing in polymeric composite structures during their operation, since they are invisible or barely visible on a surface, while inside a structure they can exist in a form of extended delaminations as well as matrix and interface cracks. According to damage tolerance and condition-based monitoring philosophies applied during maintenance of aircraft structures damage should be detected and identified in a possibly early stage of its development, especially LVIDs. The currently being developed non-destructive testing method, the self-heating based vibrothermography (SHVT), is a promising approach for damage detection and identification in polymeric composite structures, which is based on hysteretic heating of a polymeric matrix used here as a thermal excitation for the method, and is applicable especially in the cases when a direct access to a tested structure is limited or impossible. In this paper, the authors examined the sensitivity of SHVT to LVIDs considering various shapes of impactors and various impact energies. Moreover, the extended study on damage detectability enhancement was performed. The obtained results reveal acceptable detectability of LVIDs using SHVT, while the applied enhancement methods allow for a significant improvement of the damage detectability and quantification.
       
  • Numerically-based method for fracture characterization of Mode I-
           dominated two-dimensional delamination in FRP laminates
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): Aida Cameselle-Molares, Anastasios P. Vassilopoulos, Jordi Renart, Albert Turon, Thomas Keller A new numerically-based method suitable for determining the total strain energy release rate (SERR) involved in two-dimensional (2D) Mode I-dominated delamination under opening loads in FRP laminates is presented. The method is based on the mutual dependence of the load vs opening displacement curves slope exhibited after the full development of the fracture process zone (FPZ) and the total SERR involved in the delamination process. The equation relating these parameters is derived from three-dimensional finite element analyses performed using simple linear-softening cohesive zone models. Considering that the load-displacement curve reflects the overall fracture behavior, the above-mentioned slope correlates with the mean total SERR required to propagate the total 2D crack, independently of any local total SERR’s variation along the crack front. Thus, the same mean cohesive zone model is used in all directions. By substituting the corresponding experimental slope of the load-displacement curves in the derived equation the total SERR is obtained. The method was validated using the experimental results from three types of GFRP/epoxy laminates with different fiber architectures. The measurement of the crack front is not required and the method is valid for any fiber architecture, crack shape and boundary conditions in Mode I-dominated and opening loading cases.
       
  • Non-linear stability of the in-plane functionally graded (FG) plate
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): Zbigniew Kolakowski, Leszek Czechowski Gradation along the plate thickness is considered in plate structures in practice. It concerns especially issues of linear and non-linear stability of functionally graded (FG) structures. In the present work, a square in-plane FG plate made of a step-variable gradation material was assumed. A five-strip FG plate with two cases of boundary conditions: simply supported on all edges and clamped on longitudinal edges was considered. A stability problem of the FG plate subjected to compression and shear load and a non-linear issue of stability of the compressed plate was solved. To compare the results, the calculations were carried out with three methods.
       
  • Properties of a thermoplastic composite skin-stiffener interface in a
           stiffened structure manufactured by laser-assisted tape placement with
           in-situ consolidation
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): Aswani Kumar Bandaru, Gearóid Clancy, Daniël Peeters, Ronan M. O' Higgins, Paul M. Weaver A critically important consideration of stiffened structural panels is the interfacial properties between skin and stiffener. In the present study a novel implementation of laser-assisted tape placement (LATP) was used to produce a representative skin-stiffener of a wingbox from carbon fibre reinforced PEEK. First, a stiffener is manufactured using this method and subsequently the skin is attached using the same method without need for a secondary bonding process. The interfacial properties between the skin and stiffener have been characterised in terms of interlaminar shear strength (ILSS) and fracture toughness (Mode-I and Mode-II) properties. LATP laydown direction and laser power was found to influence the skin-stiffener interface Mode-I fracture toughness, but not affect the Mode-II fracture toughness. The values of ILSS and fracture toughness compare favourably with those results reported in the literature, in particular for those reported for equivalent aerospace certified CF/PEEK material (APC-2).
       
  • Numerical analysis of the vibration response of skew
           magneto-electro-elastic plates based on the higher-order shear deformation
           theory
    • Abstract: Publication date: Available online 6 February 2019Source: Composite StructuresAuthor(s): M. Vinyas, G. Nischith, M.A.R. Loja, F. Ebrahimi, N.D. Duc This work addresses the problem of the three-dimensional free vibration behavior of skew magneto-electro-elastic plates under the framework of a higher order shear deformation theory. To this end, the finite element method was adopted considering the Hamilton’s principle. The results obtained from the present finite element model are verified with the simulation results of COMSOL software. Further, a parametric study is carried out to evaluate the influence of boundary conditions, stacking sequence, aspect ratio, and the length-to-width ratio. A special emphasis has been given to the natural frequency characteristics of multiphase skew magneto-electro-elastic plates as well. The results from the present analyses allow concluding on the significant influence that the geometrical skewness has on the free vibration behavior of these plates.
       
  • Designing hierarchical metamaterials by topology analysis with tailored
           Poisson’s ratio and Young’s modulus
    • Abstract: Publication date: Available online 5 February 2019Source: Composite StructuresAuthor(s): Hang Yang, Bing Wang, Li Ma In this work, we present an innovative three-dimensional (3D) hierarchical design strategy to systematically summarize the configuration characteristics of existing cellular structures and propose a novel class of mechanical metamaterials based on topology analysis, which have tailored Poisson’s ratio and Young’s modulus. Theoretical, numerical and experimental analyses were conducted to reveal the basic mechanical properties of the metamaterials. And these results agree very well which validate the correctness of the theories. Samples of the proposed structures made of Nylon were fabricated through 3D printing technology to carry out compression tests and finite element analysis (FEA) were performed to give an insight into the mechanical response. Experimental and numerical results revealed that the proposed 3D second-order hierarchical metamaterials can achieve a series of special combinations of Poisson’s ratio in three perpendicular directions. The sign and magnitude of Poisson’s ratio can be tailored by appropriately adjusting the first and second order configurations and their geometrical parameters. Meanwhile, systemic analysis and comparison revealed that relative Young’s modulus is contingent on deformation pattern, i.e., axial-deformation dominated stiffness is much higher than bending-dominated stiffness. Similar to Poisson’s ratio, the magnitude of Young’s modulus can be tailored by geometrical parameters and first and second order configurations in a relative large range in the case of given Poisson's ratio (sign and magnitude). This work can provide useful reference for the design, fabrication and analysis of 3D metamaterials with novel properties and functions, particularly with auxetic behavior, which are promising in some technical applications.
       
  • Basalt-based fiber-reinforced materials and structural applications in
           civil engineering
    • Abstract: Publication date: Available online 5 February 2019Source: Composite StructuresAuthor(s): Elisabetta Monaldo, Francesca Nerilli, Giuseppe Vairo In the last decades, a growing interest in using basalt as reinforcement for composite materials has emerged, since promising physico-chemical and mechanical properties of basalt products, as well as good processability features and cost-effectiveness of the corresponding production technologies. In particular, basalt fibers allow to define composite materials really competitive with those obtained by employing traditional glass or carbon fibers. Recent experimental programs and analytical approaches reveal that basalt-based fiber-reinforced materials may be effective for a number of structural applications in civil engineering. Depending on the fiber treatment and arrangement, as well as on the matrix type (polymeric or cementitious) different composite materials have been conceived. For instance, strengthening and retrofitting of existing structures (both concrete and masonry) may be performed through basalt-based fiber-reinforced polymers (BFRP) and cementitious matrices (BFRCM), as well as novel design concepts can be exploited by referring to basalt-based rebars and fiber-reinforced concrete (BFRC). This paper aims to furnish a systematic review of the state of the art on basalt fibers, basalt-based composite materials and their applications in civil engineering field, by tracing main available evidence and highlighting perspective aspects and open problems.
       
  • Finite element simulation of damage in fiber metal laminates under high
           velocity impact by projectiles with different shapes
    • Abstract: Publication date: Available online 5 February 2019Source: Composite StructuresAuthor(s): Qian Zhu, Chao Zhang, Jose L Curiel-Sosa, Tinh Quoc Bui, Xiaojing Xu Fiber metal laminates (FMLs) have been widely used in many high-tech industries as protective structures because of their excellent impact resistance. The damage constitutive model that accurately characterizes the complex damage modes and failure processes of FMLs is the base to study the ballistic impact problems by numerical simulation. In this paper, a nonlinear finite element model based on continuum damage mechanics is established to investigate the damage modes and failure mechanisms of carbon fiber reinforced aluminum laminates (CRALLs) under high velocity impact. Johnson-Cook material model and a 3D rate-dependent constitutive model are applied to identify the in-plane damage in aluminum and fiber composite layers respectively; cohesive elements governed by bilinear traction-separation constitutive model are implemented to simulate the inter-laminar delamination induced by impact. The ballistic performance and damage characteristics of CRALLs under high velocity impact by projectiles with different shapes are studied in detail. The obtained numerical results correlate well with the available experimental data thus validates the proposed finite element model, which also provides an appropriate reference for numerical studies of high velocity impact issues in other FMLs.
       
  • Δ K eff 1 - α K max α +for+fatigue+crack+propagation+in+prestressed-CFRP-repaired+steel+structure&rft.title=Composite+Structures&rft.issn=0263-8223&rft.date=&rft.volume=">A novel driving force parameter Δ K eff 1 - α K max α for
           fatigue crack propagation in prestressed-CFRP-repaired steel structure
    • Abstract: Publication date: Available online 5 February 2019Source: Composite StructuresAuthor(s): Huawen Ye, Wang Tianqi, Chun Shuai, Changmeng Liu, XunXu A study was numerically and experimentally conducted to investigate the crack driving mechanism of steel structures strengthened with non- and prestressed CFRP (Carbon Fiber-reinforced Polymer) plates. A novel and simple crack driving force model using ΔKeff and Kmax was established to account for the interplay of cyclic and monotonic damage by introducing a correlation factor to define their contribution. The extensive crack growth curves of tensile fatigue testing under constant amplitude loading were referred to in the literature, and finite element method (FEM) modeling was performed to calculated the stress intensity factors (SIF) of the specimens. The relationship between the correlation factor and stress ratio (R-ratio) was determined by the reverse-reasoning method through the remaining life in the experimental data. Then the fatigue tests of different steel elements, including tensile plate, I-section and RHS beam, were used to verify the prediction accuracy. These results validated the proposed method that provides much higher accurate estimation of the remaining fatigue life at a wide range of R-ratios comparing to the traditional methods, such as crack closure model and two crack driving force model.
       
  • Free vibration analysis of annular sector sandwich plates with FG-CNT
           reinforced composite face-sheets based on the Carrera’s Unified
           Formulation
    • Abstract: Publication date: Available online 4 February 2019Source: Composite StructuresAuthor(s): Nasrin Naderi Beni This paper presents an investigation of the free vibration of annular sector sandwich plates with carbon nanotube reinforced face-sheets and various edges boundary conditions. It is assumed that carbon nanotubes are radially aligned and distributed uniformly (UD) or functionally graded (FG) in the thickness direction. The effective material properties of CNT reinforced face-sheets are estimated using the extended rule of mixture, which contains efficiency parameters to consider the size-dependent material properties. A variable kinematic model which has been utilized for FGM cases is extended to FG-CNTs to describe the continuous variation of properties through the thickness. In this paper, the Carrera’s Unified Formulation (CUF) is developed for the analysis of asymmetric sector plates for the first time. The governing equations and associated boundary conditions are obtained employing the Principle of Virtual Displacements (PVDs) based on the CUF and solved using the generalized differential quadrature (GDQ) method. Numerical results for some special cases are presented and validated by comparison with available results in the literature. Some numerical results are tabulated to show the effects of the volume fraction of carbon nanotubes, boundary conditions and geometrical parameters on the free vibration behavior of the annular sector sandwich structures with CNTRC face-sheets.
       
  • Mechanical properties and energy absorbing capabilities of Z-pinned
           aluminum foam sandwich
    • Abstract: Publication date: Available online 2 February 2019Source: Composite StructuresAuthor(s): Sajjad Raeisi, Javad Kadkhodapour, Andres Tovar Aluminum foam sandwich (AFS) structures are suitable for impact protection in lightweight structural components due to their specific energy absorption capability under compression. However, tailoring the deformation patterns of the foam cells is a difficult task due to the randomness of their internal architecture. The objective of this study is to analyze the effect of embedding aluminum pins into an AFS panel (Z-pinning) to better control its deformation pattern and improve its energy absorption capability. This study considers a closed-cell AFS panel and analyzes the effect of multi-pin layout parallel to the direction of the uniaxial compressive loading. The results of the experimental tests on the reference (without Z-pinning) AFS are utilized to develop numerical models for the reference and Z-pinned AFS structures. Physical experiments and numerical simulations are carried out to demonstrate the advantages of Z-pinning with aluminum pins. The results exhibit a significant increase in elastic modulus, plateau stress and energy absorption capability of the Z-pinned samples. Also, the effect of the pin size and Z-pinning layout on the mechanical performance of the Z-pinned AFS is also investigated using numerical simulations.
       
  • An isogeometric Bézier finite element analysis for piezoelectric FG
           porous plates reinforced by graphene platelets
    • Abstract: Publication date: Available online 2 February 2019Source: Composite StructuresAuthor(s): Lieu B. Nguyen, Nam V. Nguyen, Chien H. Thai, A.M.J. Ferreira, H. Nguyen-Xuan In this study, we for the first time present an isogeometric Bézier finite element formulation for bending and transient analysis of functionally graded porous (FGP) plates reinforced by graphene platelets (GPLs) embedded in piezoelectric layers. We name it as PFGP-GPLs for short. The plates are constituted by a core layer, which contains the internal pores and GPLs dispersed in the metal matrix either uniformly or non-uniformly according to three different patterns, and two piezoelectric layers perfectly bonded on the top and bottom surfaces of host plate. The modified Halpin–Tsai micromechanical model is used to estimate the effective mechanical properties which vary continuously along thickness direction of the core layer. In addition, the electric potential is assumed to vary linearly through the thickness for each piezoelectric sublayer. A generalized C0-type higher-order shear deformation theory (C0-HSDT) in association with isogeometric analysis (IGA) based on Bézier extraction is investigated. Our approach allows performing all computations the same as in the conventional finite element method (FEM) yet the present formulation shows more advantages. The system of time-dependent equations is solved by the Newmark time integration scheme. The effects of weight fractions and dispersion patterns of GPLs, the coefficient and distribution types of porosity as well as external electrical voltages on structure’s behaviors are investigated through several numerical examples. These results, which have not been published before, can be considered as reference solutions for future works.
       
  • Free Vibration Analysis of Sandwich Conical Shells with Fractional
           Viscoelastic Core
    • Abstract: Publication date: Available online 2 February 2019Source: Composite StructuresAuthor(s): M.R. Permoon, M. Shakouri, H. Haddadpour The vibration characteristics, including fundamental frequencies and loss factors, of a sandwich conical shell with constrained viscoelastic layer is presented. The mechanical properties of viscoelastic core is modeled using Zener fractional order model. The equations of motion are derived employing Donnell representation of classical shell theory and solved using Raighly-Ritz method. The results are compared with other investigations and the effects of geometric parameters including the length to radius, radius to thickness and core to facing thickness on fundamental frequencies and loss factors are studied.
       
  • Strain rate effect on the mechanical behavior of polyamide composites
           under compression loading
    • Abstract: Publication date: Available online 2 February 2019Source: Composite StructuresAuthor(s): Abdellah Massaq, Alexis Rusinek, Maciej Klosak, Mohamed Slim Bahi, Angel Arias This paper presents an experimental study on the effect of strain rate on the compressive behavior of polyamide composites. Contrary to thermoset woven reinforced composites, thermoplastic woven reinforced composites have always received less interest despite its excellent damage and impact resistances. In this context, this work aims to study the behavior of fiber reinforced thermoplastic composites submitted to high strain rate in compression. The tested material is a thermoplastic composite made of armor tissue of equilibrate glass fiber and the matrix is composed of Polyamide 6 (PA6/Glass). The material is prepared with the fibers woven in 0/90 direction.The compressive mechanical response of PA6/Glass composite was determined in the transverse and longitudinal fibers directions at quasi-static and high strain rates.The hydraulic machine and Split Hopkinson Pressure Bar experiments were conducted to determine the dynamic and quasi static compressive deformation and fracture of the PA6/Glass at strain rates from 10-5 s-1 to 1 s-1and 100 s-1 to 2500 s-1, respectively.In this work, the main goals were to determine the strain rate effect on: elastic modulus, failure stress and failure energy as a function of the loading direction. The strain rate sensitivity of the failure stress level and failure energy were observed. In addition, the failure mechanism was characterized by examining the fracture surfaces using the scanning electron microscopy (SEM) method.In quasi-static conditions of loading, the material reached its capacity due to the formation of shear bands, that concerned all three tested compression directions. In dynamics, the failure took place by shearing followed by delamination. In case of dynamic loading in the direction perpendicular to fibers, the observations made by SEM showed that the failure of the composite had a fragile nature.
       
  • Peridynamic Modeling of Lamb Wave Propagation in Bimaterial Plates
    • Abstract: Publication date: Available online 1 February 2019Source: Composite StructuresAuthor(s): Reza Alebrahim In this study the nonlocal bond-based Peridynamic (PD) theory was applied to simulate Lamb wave transmission in 2D bimaterial plates. Plates of unlike materials were jointed end-to-end to make a bimaterial plate. The surface of the plate was then excited tangentially by single-frequency and multi-frequency force signals. The influence of changing material properties on travelling of the symmetric and antisymmetric Lamb waves were studied in detail. The phase and group velocities of travelling wave in bimaterial plates were calculated and it was found that dissimilar material properties of two joint plates can significantly alter the amplitude and arrival time of the wave. Moreover, Fast Fourier Transform (FFT) of the time history of symmetric Lamb wave velocity was calculated and verified. Accuracy and consistency of PD wave model was confirmed entirely using Spectral Finite Element Method (SFEM). The comparison between the results of two applied methods shows a good agreement.
       
  • High-performance analysis of the interaction between plate and
           multi-layered elastic foundation using SBFEM-FEM
    • Abstract: Publication date: Available online 31 January 2019Source: Composite StructuresAuthor(s): Wenbin Ye, Jun Liu, Hongyuan Fang, Gao Lin The scaled boundary finite element method (SBFEM) coupled with the finite element method (FEM) for the simulation of the interaction problem between the elastic plate structure and the multi-layered unbounded elastic soil is first developed in this paper. First, the whole system is subdivided into three sub-domains, including the semi-infinite far-field system, the near-field sub-domain, and the plate structure. The far field of the soil is modeled by utilizing the modified scaled boundary finite element method with a scaling line instead of the scaling center used in the traditional SBFEM. In the traditional SBFEM, only the boundary is discretized with surface elements, so the spatial dimension is reduced by one, and the final governing equation can be solved analytically in the radial direction of the scaled coordinate system, and it can exactly meet the infinite domain problem. The stiffness matrix of the three-dimensional (3D) near field is obtained using the standard FEM. The SBFEM is also applied in order to simulate the deformation characteristics of the plate structure based on the 3D elastic equation without introducing any assumption of the thin plate theory, and the high-order spectral element is introduced in order to discretize the middle surface of plate so that the complicated curved boundaries can be better represented. Then, according to the principle of the degree of freedom matching at the same node, the global stiffness matrix of the plate-soil system can be obtained by coupling the stiffness matrices of the sub-domains at the far-field/near-field interface, as well as at the plate/near-field interface. Thus, the response of the whole system under the external load can be solved naturally. Four numerical examples, consisting of a square plate resting on an isotropic soil, multi-layered soil with weak and thin interlayer, a plate with a different geometrical shape and a square plate with a hole, are provided in order to validate the accuracy and versatility of the proposed formulations.
       
  • Formability, defects and strengthening effect of steel/CFRP structures
           fabricated by using the differential temperature forming process
    • Abstract: Publication date: Available online 31 January 2019Source: Composite StructuresAuthor(s): Yuqin Guo, Changpan Zhai, Fuzhu Li, Xinfeng Zhu, Fan Xu, Xuelian Wu Steel/CFRP materials consisting of steel sheets and CFRP prepregs are attracting more and more attention as the development of new energy vehicles requiring strongly weight reduction as well as the cost reduction of available constituent materials. This study is the first to propose the differential temperature forming process to fabricate steel/CFRP structures. The successful fabrication for steel/CFRP U-shape and box-shape structures demonstrates the excellent forming capability of the used forming process for steel/CFRP materials. Moreover, the steel/CFRP U-shape structures is found to possess a higher forming precision than their pure steel counterparts due to the smaller springback. For the steel/CFRP box-shape structure, the typical forming defects and their formation mechanisms are analyzed in detail. Finally, the steel/CFRP U-shape and box-shape structures are validated to have much higher load-carrying capability and better energy absorption property than their single material counterparts by crushing tests. Furthermore, the steel/CFRP U-shape structure can obtain more obvious strengthening effect compared to the steel/CFRP box-shape structure. So, they are particularly suitable for serving as the load-carrying channel parts widely used in automobile industry.
       
  • Nonlinear free vibration of geometrically imperfect functionally graded
           sandwich nanobeams based on nonlocal strain gradient theory
    • Abstract: Publication date: Available online 31 January 2019Source: Composite StructuresAuthor(s): Hu Liu, Zheng Lv, Han Wu This paper is devoted to examining the nonlinear vibrational behaviors of functionally graded (FG) sandwich nanobeams in the presence of initial geometric imperfection. Based on the nonlocal strain gradient theory, the governing equation of the FG sandwich nanobeam with consideration of the Von-Karman nonlinearity and initial geometric imperfection is derived. The nonlinear oscillator frequency is obtained with the aid of He’s variational principle. Three types of nanobeams, i.e., FG nanobeam (Type A), sandwich nanobeam with homogeneous core and FG skins (Type B), and sandwich nanobeam with FG core and homogeneous skins (Type C) are taken into account. A cosine function similar to the mode shape form is employed to describe the geometric imperfection mode. Firstly, the present theoretical model is verified by comparing with previous perfect FG sandwich beams. Then, several key parameters such as the power-law exponent, the amplitudes of the nonlinear oscillator and the geometric imperfection, as well as the nonlocal and material characteristic parameters are investigated in detail. Finally, apart from the structural types, the influence of thickness distribution scheme is also thoroughly elucidated. The results obtained in this paper are helpful for exploring the FG sandwich design to enhance the mechanical performance of nano-devices.
       
  • Free vibration analysis of bidirectional-functionally graded and
           double-tapered rotating micro-beam in thermal environment using modified
           couple stress theory
    • Abstract: Publication date: Available online 30 January 2019Source: Composite StructuresAuthor(s): Sujash Bhattacharya, Debabrata Das Free vibration behavior of bidirectional-functionally graded, double-tapered rotating micro-beam is investigated. An improved mathematical model based on Timoshenko beam theory and modified couple stress theory is developed that includes the effects of geometric non-linearity, spin-softening, Coriolis acceleration and high operating temperature. The problem is formulated in two steps. In the first step, the problem involving time-invariant inertia force due to rotation of the beam with constant angular speed is formulated using minimum potential energy principle and the governing non-linear equations are solved employing an iterative algorithm. In the next step, the free vibration problem is formulated employing Hamilton’s principle and using the tangent stiffness of the deformed configuration induced due to time-invariant inertial loading. The governing equations for free vibration are transformed to state-space to formulate an eigenvalue problem. The governing equations are solved by approximating the displacement fields following Ritz method. The model is successfully validated with the available results. Extensive sets of results are presented for the first two chord-wise and flap-wise modes of vibration in non-dimensional speed versus frequency plane. The effects of different parameters such as size-dependent thickness, axial and thickness gradation indices, taperness parameters, hub parameter, length-thickness ratio, operating temperature and FGM composition are reported.
       
  • A Review on Optimization of Composite Structures Part II: Functionally
           Graded Materials
    • Abstract: Publication date: Available online 30 January 2019Source: Composite StructuresAuthor(s): S. Nikbakht, S. Kamarian, M. Shakeri Functionally Graded (FG) structures are a novel design through which the material properties vary smoothly and this feature leads these structures to have better mechanical or thermal performances. They are mostly constituted from two or more materials with gradually varying volume fraction distribution. Most of the publications on the optimization of laminated composite structures were investigated in the first part of the authors’ review paper [1]. In this research which acts as the second part, the majority of publications on optimization of FG structures are reviewed. In addition to FG beams, plates and shells, various structures such as tubes, implants, rotating disks, sport instruments, etc. are investigated. Furthermore, the key outputs of each publication are represented to make this article an asset source for mechanical engineers since there has not been any comprehensive review article on optimal designs of FG structures in the literature.
       
  • Assessment of a damage model for wound composite structures by acoustic
           emission
    • Abstract: Publication date: Available online 29 January 2019Source: Composite StructuresAuthor(s): Juan Pedro Berro Ramirez, Damien Halm, Jean Claude Grandidier This paper deals with the link between the acoustic activity due to damage in wound composite structures and the simulated evolution of damage variables. A damage model able to accurately capture the different degradation modes which may occur in this type of material is first selected. A parallel is drawn between the continuous evolution of the damage variables and the discrete acoustic events. The mechanical behavior of notched samples made of two different wound composite lay-ups and involving complex damage combinations are simulated and compared to acoustic emission. The satisfactory correlation confirms the physical meaning of the damage variables and validates the model assumptions. The association of experimental acoustic signals and a damage model is a tool to understand the degradation scenario of wound composite structures and the meaning of the recorded acoustic events.
       
  • Parametric study on the buckling load after micro-bolt repair of a
           composite laminate with delamination
    • Abstract: Publication date: Available online 29 January 2019Source: Composite StructuresAuthor(s): Gyu-Seok Kang, Byeong-Su Kwak, Hyeon-Seok Choe, Jin-Hwe Kweon Repair of a composite laminate with delamination using micro-bolts is studied parametrically. The effects on compressive buckling load of delamination crack length, bolt material, bolt diameter and arrangement, and bolt–laminate clearance are considered. For 45- and 65-mm crack lengths, buckling load recovery rates using brass bolts are 90% and 73%, respectively. Using steel increases the rate by 6.6% compared to the intact specimen. Tests are performed fixing the number of steel bolts for bolt diameters of 0.6, 1.0, and 1.2 mm. The buckling load recovery rate using 1.2- versus 0.6-mm bolts increases by 6.8%. Finite element analysis confirms the effect of the bolt–laminate gap: 27% larger buckling load for no clearance than for a 0.1-mm gap. 18% higher buckling load, which is 97% of intact-specimen buckling load, is obtained for a 1.2-mm-diameter bolt repair by gluing bolts and holes and then tightening them compared with using bolts alone.
       
  • Mechanical behaviors of C/SiC pyramidal lattice core sandwich panel under
           in-plane compression
    • Abstract: Publication date: Available online 28 January 2019Source: Composite StructuresAuthor(s): Yanfei Chen, Lu Zhang, Yunong Zhao, Rujie He, Shigang Ai, Liqun Tang, Daining Fang C/SiC composite lattice-core sandwich panels combined with thermal insulation and load-bearing capacities are considered as the most promising candidates for thermal protection system (TPS). In this study, C/SiC pyramidal lattice-core sandwich panel with different inclination angles were fabricated using a compression molding and precursor infiltration and pyrolysis (PIP) method. In-plane compressive experiments are conducted to study the failure behavior of these sandwich panels. The analytical failure modes including Elastic buckling, face sheet wrinkling, face sheet crushing and interlayer delamination are established to construct the mechanism maps. The effect of geometrical parameters on failure modes are symmetrically and analytically studied. Due to the limits of the cost, virtual tests are supplemented by finite element method (FEM). Face sheet crushing is experimentally observed for almost all specimens with different inclination angles, which is in good agreement with analytical predictions. Numerical simulation results show that interlayer delamination occurs at the attachment between face sheet and lattice core after elastic buckling and core shear buckling. This paper gives us some fundamental understanding of the mechanical response and failure mechanism of C/SiC composite lattice-core sandwich panels.
       
  • Effect of hybridization on the impact properties of flax/basalt epoxy
           composites: influence of the stacking sequence
    • Abstract: Publication date: Available online 28 January 2019Source: Composite StructuresAuthor(s): M.R. Ricciardi, I. Papa, V. Lopresto, A. Langella, V. Antonucci The effect of stacking sequence on the impact damage mechanisms and the matrix-fiber dependent properties, such as flexural and interlaminar strength, of epoxy hybrid basalt/flax composites has been experimentally investigated. The basalt and flax fabrics have been appropriately selected with approximately the same areal weight and stacked in the same number in three different symmetrical analysed configurations to manufacture composites with comparable conditions regarding fibre content by weight. No influence of fibre sequence was observed for the flexural modulus, whereas some differences were exhibited by the flexural and the interlaminar shear strength depending on the resin content. The impact tests were carried out at penetration and different energy levels. After impact, indentation measurements have been performed by a confocal microscope to get information on the damage propagation and characteristics that resulted affected by the hybridisation type and by the impact energy. The results evidenced the relevance of the stacking sequence in the composite design to meet specific requirements.
       
  • On the fracture behaviour of adhesively bonded CFRP hat-shaped thin-walled
           beam under axial crushing load: An experimental and modelling study
    • Abstract: Publication date: Available online 28 January 2019Source: Composite StructuresAuthor(s): Xiao Han, Shaoqiang Hou, Liang Ying, Wenbin Hou, Husniddin Aliyev Thin-walled beams are widely adopted as the key frontal energy absorption component in automotive body. This work focused on the numerical modelling of a CFRP hat-shaped thin-walled beam under axial-crushing load, which was well validated against testing data as well as experimentally observed fracture behaviour. CFRP hat beam was manufactured with prepreg IM7/8552 through hot-press moulding, and then bonded with a base plate using structural adhesive. The adhesively bonded CFRP beam was loaded under axial crushing to investigate the fracture behaviour in CFRP as well as adhesive layer. The crushing process of CFRP beam was numerically modelled, where the strength-based Chang-Chang failure criterion was adopted to determine the fracture property of CFRP, while Tiebreak was attached in the adhesive and matrix to simulate the interfacial and interlaminar failure. Experimental work revealed that obvious interlaminar failure was observed in CFRP beam, with the outer layers curving outward and inner layers bending inward. Numerical modelling showed good agreement with the experimental data in the aspects of initial peak load and energy absorption. Based on the developed modelling technique, the fracture behaviour in CFRP beam as well as the interfacial failure in adhesive layer and composite matrix can be well predicted and evaluated.
       
  • Mesoscale modelling of damage in half-hole pin bearing composite laminate
           specimens
    • Abstract: Publication date: Available online 14 January 2019Source: Composite StructuresAuthor(s): Fujian Zhuang, Puhui Chen, Albertino Arteiro, Pedro P. Camanho This paper presents the development and validation of a mesoscale numerical model for predicting the bearing damage and failure of composite laminates reinforced by unidirectional fibers. Firstly, half-hole pin bearing tests were carried out on composite laminates with both quasi-isotropic and soft lay-ups, as well as in specimens with variations in ply thickness and stacking sequence, using multiple measurement and inspection tools for a comprehensive characterization of the damage mechanisms. Then, three dimensional (3D) finite element models with fiber-aligned mesh for composite plies and considering various frictional contacts were built to simulate the bearing tests using a commercial explicit solver. The embedded material model incorporated 3D phenomenological invariant-based failure criteria using in situ ply strengths, mechanism-based continuum damage models (longitudinal bi-linear damage model and transverse smeared crack model) for intralaminar damage, and the cohesive zone model for interlaminar damage. Finally, detailed analyses and comparisons of the experimental and numerical results were performed in both macroscopic mechanical behavior and mesoscale failure mechanisms, where a good correlation was observed. Sensitivity studies on the effect of the modelling parameters on the post-peak response prediction were also conducted, providing relevant guidelines to identify future research directions.
       
 
 
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